Hormones are secreted by

Options

A. All living organisms
B. Vertebrates only
C. Inverterbrates
D. All metazoans

Answer

**Step-by-Step Solution:**

1. **Understanding Hormones**: Hormones are chemical substances that act as messengers in the body, regulating various physiological processes and functions.

2. **Source of Hormones**: Hormones are secreted by specialized glands known as endocrine glands. These glands release hormones directly into the bloodstream.

3. **Presence of Hormones in Organisms**: Hormones are not exclusive to one group of organisms. They are found in a wide variety of living organisms, including both vertebrates and invertebrates.

4. **Definition of Metazoans**: Metazoans are multicellular organisms whose bodies are composed of cells that are organized into tissues and organs. This includes a vast array of organisms, such as mammals, birds, reptiles, amphibians, and fishes.

5. **Conclusion**: Given that hormones are secreted by all metazoans, the correct answer to the question "Hormones are secreted by" is "all metazoans."

**Final Answer**: Hormones are secreted by all metazoans.

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